The present invention relates to methods and apparatus for creating small (micron and smaller) holes in transparent materials for the purpose of drilling, cutting, separating, perforating, or otherwise processing the materials, and, more particularly, to the arrangement of these holes to arrest crack propagation in the transparent materials.
In recent years, precision micromachining and its improvement of process development to meet customer demand to reduce the size, weight and material cost of leading-edge devices has led to fast pace growth in high-tech industries in flat panel displays for touch screens, tablets, smartphones and TVs, where ultrafast industrial lasers are becoming important tools for applications requiring high precision.
There are various known ways to cut glasses. In conventional laser glass cutting processes, the separation of glass relies on laser scribing or perforation followed by separation with mechanical force or thermal stress-induced crack propagation. Nearly all current laser cutting techniques exhibit one or more shortcomings, including: (1) limitations in their ability to perform a free form shaped cut of thin glass on a carrier due to a large heat-affected zone associated with the long laser pulses (nanosecond scale or longer) used for cutting; (2) production of thermal stress that often results in cracking of the glass surface near the region of laser illumination due to the generation of shock waves and uncontrolled material removal; (3) difficulties in controlling the depth of the cut (e.g., to within tens of microns); and/or (4) creation of sub-surface damage in the glass that extends hundreds of microns (or more) glass below the surface of the glass, resulting in defect sites at which crack propagation can initiate.
These micro-cracks, for example, most typically form at the edges of the glass, and the crack can then propagate into the bulk of the glass. While there are different techniques to deal with crack propagation, such as ion-exchange used to create a compressive stress (“CS”) at the edge of the glass sheet, these techniques are expensive and ineffective. Accordingly, there is a need to improve glass strength and stability by preventing or arresting crack propagation.